For more than a decade now a great deal of attention has been focused on the hazards of bacterial, fungal, and viral contamination from everyday exposures. What once was a primary concern for health care facilities, especially hospitals, and food processing/food preparation facilities, is now an everyday concern for most every business, the home, schools, public transportation and so on. More virulent and, oftentimes, drug resistant strains of pathogenic bacteria are being identified around the globe. And, while such issues were once considered localized issues, they are now regional, nationwide, if not world-wide issues owing to the ease and extent to which the people of the world travel, not to mention the world-wide market place for manufactured goods and, perhaps more critically, produce and other foodstuff.
While pathogenic bacteria are certainly a major concern, they are not the only concern. The world is flush with microorganisms that may not cause death or sickness; yet they impose upon or adversely impact our lives on a daily basis. For example, molds can create an unsightly appearance in or on our homes, especially in bathrooms and basements; certain bacteria may affect the smell and/or taste of our drinking water, other bacteria affect the smell of clothing, towels, upholstery and other fabrics, etc.
Numerous efforts have been undertaken to ward off contamination and/or transmission of such bacteria, fungi and other microorganisms. Specifically, much effort has been made to introduce antimicrobial performance into a host of specialized and non-specialized products and articles of manufacture, especially those comprising or associated with touch surfaces. Such products and articles run the gamut, from cutting boards to refrigerator linings, from door knobs to cellular telephone housings, from HVAC units and components to medical devices such as stents, catheters and the like, from fabrics to wound care products, etc. This antimicrobial performance is achieved by either treating the surface of the product or article with a coating containing an antimicrobial agent or directly incorporating the antimicrobial agent into the material or composition from which the product or article is made.
While many of these applications have achieved varying degrees of commercial and technical success, one particular application, fabrics, especially for apparel, has and continues to be an area of continual developmental effort. Early on, manufacturers employed organic antimicrobial agents, most frequently triclosan, as an antimicrobial agent applied as a topical treatment or, more commonly, incorporated into the polymer melt from which the fibers/filaments are spun/extruded. However, the ability to incorporate triclosan into fiber materials is limited: showing success in acrylic and/or acetate fibers but not in polyamides, polyesters, etc. The use of triclosan has also raised certain health and safety concerns, especially with respect to skin irritation and sensitivity to the chlorine and chlorides within these compounds as well as the possible bioabsorption of the triclosan and/or its components/degradation residues into the body. Furthermore, triclosan has poor longevity in these applications due to its mobility in polymer compositions and the quickness with which it is washed out of the fabric.
The antimicrobial properties of a number of inorganic materials, especially metals such as silver, copper, zinc, mercury, tin, gold, lead, bismuth, cadmium, chromium and thallium, have long been known. Certain of these metals, especially silver, zinc, gold and copper, have enjoyed greater success due to their relatively low environmental and toxicological effects and high antimicrobial activity. In order to address some of the aforementioned problems with organic antimicrobial agents like triclosan, others have taken the approach of coating fibers, filaments and/or fabric with silver metal by, for example, vapor deposition or other plating techniques. These methods bind the silver metal to the surface of the polymer fiber/filament. Antimicrobial performance arises from the relatively slow oxidation of the surface of the silver metal and the subsequent availability/release of antimicrobially active silver ions from the oxidized silver. Although effective and long lived, antimicrobial performance is poor to marginal owing to the slow rate at which the silver ions are generated: effectiveness being a function of the extent of ion generation and, hence, the rate of oxidation.
Further compounding the efficacy of silver metal is that fact that washing of the substrate or substrate surface removes all or substantially all of the oxidized silver. Consequently antimicrobial efficacy following washing is delayed until a sufficient level of oxidation or other generation of silver ions occurs on the surface of the silver metal coating Speed of oxidation is not the only concern; the costs of these silver coated materials are relatively high—though one can regulate the costs, at the expense of performance, by using less silver coated fiber in the fabric. Furthermore, fabrics made with these materials oftentimes have associated therewith a static nuisance owing to the electrical conductivity of the silver fibers. Finally, as would be expected, the presence of the silver coated fibers affects the color and feel of the fabric. Since these fibers do not absorb the dyes used to color the fabric, they will always stand out. The degree of their impact on the color or visual image depends upon the content of silver coated fiber in the fabric.
In an effort to address many of the aforementioned consequences and shortcomings of silver metal and organic antimicrobial agents, recent attention has been focused on the use of certain inorganic silver compounds, complexes and the like. Suitable inorganic silver antimicrobial agents may take many different forms including simple silver salts or complexes including wholly inorganic salts as well as organometallic complexes. Other, and especially beneficial, complex forms include those antimicrobial agents comprising ceramic particles having ion-exchanged silver ions carried therein or thereon as well as water soluble glasses that have incorporated therein various readily soluble silver ion sources. Exemplary ion-exchange type antimicrobial agents include those wherein the ion-exchange carrier particles are ceramic particles including zeolites, hydroxy apatites, zirconium phosphates and the like. Antimicrobial agents based on zeolite carriers are disclosed in, for example, U.S. Pat. Nos. 4,911,898; 4,911,899; 4,938,955; 4,906,464; and 4,775,585. Antimicrobial zirconium phosphates include those disclosed in, for example, U.S. Pat. Nos. 4,025,608 and 4,059,679 and the Journal of Antibacterial Antifungal Agents Vol. 22, No. 10, pp. 595-601, 1994. Finally, antimicrobial hydroxyapatites powders include those disclosed in U.S. Pat. Nos. 5,009,898 and 5,268,174, among others.
Although these antimicrobial agents have found growing success in the production of antimicrobial fabrics and enable excellent antimicrobial performance, generally without the delay of the silver metal coated fibers, they still have some of the same shortcomings as well as some additional problems. For example, except for hydrophilic polymers, when the antimicrobial agent is incorporated into the original polymer material from which the fiber or fabric is made, only that portion of the antimicrobial agent at or proximate to the surface of the fiber or filament made thereof is available to provide antimicrobial efficacy. Specifically, because these agents rely upon contact with water or moisture to release and transport the antimicrobial silver ion, unless there are pores in the polymer or the polymer has hydrophilic characteristics, there are no transport pathways for the ions from within the polymer Consequently, with hydrophobic or insufficiently hydrophilic amphiphilic materials, the manifestation of antimicrobial efficacy is limited to those antimicrobial agents in contact with the surface of the fibers. Thus, depending upon the denier of the fibers, there is the possibility that much of the antimicrobial agent may be wasted and non-accessible, thereby adding costs without benefit. Of course, this detriment is mitigated somewhat in those fabrics which are employed in applications that are subject to wear because the erosive effect of wear will expose previously entombed antimicrobial agent. But, then again, wear also means that the integrity of the fiber itself, especially its strength and, in clothing, insulating property and appearance will be adversely affected. While the issue of longevity is less of a concern for “single-use” disposable type articles or infrequently laundered articles such as curtains, upholstery, etc., it is especially critical and of concern for fabrics used in apparel that is likely to be washed quite frequently, if not following each use. Regardless, antimicrobial efficacy is limited inasmuch as only those antimicrobial metal ion sources that are exposed are available to provide antimicrobial metal ions for antimicrobial performance. This compares with those fibers, filaments and the like that are made with sufficiently hydrophilic polymers which enable ion transport from within and throughout the fiber material. Here, all of the antimicrobial agent, even that entombed within the polymer, is available to contribute ions to antimicrobial performance. Thus, less antimicrobial agent is required to achieve the same level of efficacy in hydrophilic materials as compared to hydrophobic or insufficiently hydrophilic amphiphilic materials.
Another shortcoming of the inorganic silver antimicrobial agents, particularly those comprising the simple silver salts and other highly soluble silver antimicrobial agents, is their short-lived nature. Because of the limited amount of antimicrobial agent at the surface, a high degree of solubility means that the full amount of antimicrobial active at the surface can quickly be washed away or otherwise depleted. In hydrophilic materials, some of this loss is mitigated by ion transport of ions from within the polymer: though transport, and hence release, is limited by the rate of ion transport. And, as noted above, in all applications, those fibers that are subject to wear will seemingly replenish as the entombed antimicrobial agent is exposed at the surface of the fibers and filaments; however, again, that which is newly exposed is quickly depleted as well. Furthermore, because wear is not typically even, replenishment only affects those areas subject to constant wear. Thus, in the absence of a constant and even wear, which also means limited life to the fabric; antimicrobial efficacy slowly lessens over time as the exposed antimicrobial source is depleted.
In following, degree of performance and longevity of performance, especially as relates to wash-durability, have long been of notable concern. Numerous efforts have been undertaken and incremental advances have been made to address these issues. U.S. Pat. No. 6,607,994 points out that fabric treatments endowing particular characteristics or activity are highly desired by the apparel, home furnishings, and medical industries but conventional processes used to impart such characteristics often do not lead to permanent effects. Laundering or wearing of the treated fabric causes leaching or erosion of the agents responsible for imparting the desired characteristics. Attempts to address the problem by using encapsulated nanoparticles that form covalent bonds to the fabric have had limited success and, besides, functionalizing the nanoparticles and then chemically bonding them to the fabric adds complexity and cost and is not suitable for most applications, particularly not for broad scale consumer application in, e.g., clothing, bedding, upholstery, and the like.
Trogolo et. al., U.S. Pat. No. 6,436,422, employed hydrophilic polymer coatings so as to enhance longevity by ensuring that all of the antimicrobial agent within the coating is available for providing antimicrobial efficacy. However, hydrophilic polymer fibers and hydrophilic polymer coated fibers have limited use due to the relatively poor physical and performance properties of the hydrophilic polymer materials themselves.
Hendriks et al., U.S. Pat. No. 7,754,625, made improvements in wash durability by using an antimicrobial agent that combined a water-soluble zinc salt such as zinc oxide, and an antimicrobial metal ion source of silver and copper ions. They tested white polyester fabric and focused on discoloration of the fabric. The samples showed good bioefficacy even after several wash cycles. This represented significant progress towards the problem but, it turns out, was not universal and encounters issues with certain fabrics and/or dyed fabrics.
Specifically, it has now been found that certain chemicals or species of chemicals that are inherently present in fibers or that are incorporated and/or applied to fibers and fabrics have an adverse effect on ionic antimicrobial metals. In this regard, it is uncommon for a fabric not to be subjected to some treatment either prior to or after incorporation into an article of manufacture. Common treatments include dyes, sizings, etc. Dying is perhaps the most common treatment with sulfur dyes and indigo a couple of the most widely used dyes. Sulfur dyes are so named because of the use of sulfur in their synthesis. They are commonly used in the dying of cellulosic materials, especially cotton, and are typically associated with dark colors such as blacks, browns and deep blues. C.I. Sulfur Black 1 is an example of a sulfur dye. Denim, perhaps one of the most ubiquitous fabrics of the day, is typically dyed with indigo, alone, or more commonly, with both indigo and a sulfur dye. Due to growing concerns with the use of indigo dyes, especially from an environmental perspective, sulfur dyes are becoming even more critical and prolific in the dying of denim with sulfur dyes soon expected to surpass indigo as the key denim dye.
Although desirable and, oftentimes, necessary such treatments can further complicate the ability to impart antimicrobial activity to fabrics and articles made therefrom. Specifically, these treatments are found to contain chemical compounds which or whose degradation or oxidation products interfere with the antimicrobial agent, oftentimes chemically binding the metal ions so as to render them unavailable for antimicrobial performance. This is especially so with sulfur containing treatments, especially sulfur dyes. Although its exact mechanism of action is uncertain, it is believed that the sulfur binds with and/or complexes with the antimicrobial metal ions: thereby negating their antimicrobial efficacy.
However, this issue is not just limited to treated or dyed fabric. Indeed, certain fibers and fabrics, most especially wool and fabrics made of or containing wool, manifest poor, if any, antimicrobial efficacy following treatment with antimicrobial metal ion type antimicrobial agents. Further investigation has found that these fibers, most especially wool, naturally contain chemical compounds or species, particularly sulfur and sulfur containing compounds: thus, suffering the same consequence of dyes and treatments containing like compounds and species.
Thus, while considerable effort has been expended in the development of antimicrobial and anti-odor treatments for fabrics, problems continue. This is especially so for fabrics that are treated with and/or otherwise contain sulfur, especially sulfur dyes.
Thus, there remains a need in the industry for a fabric that provides long lasting antimicrobial and/or anti-odor performance, especially such performance with wash durability. In particular, there is a need for sulfur containing or treated fabrics that have long term antimicrobial and/or anti-odor properties which are not compromised or, if compromised, are minimally compromised by washing, particularly repeated washing
There also remains a need for a method, especially a simple and cost effective method, by which antimicrobial and/or anti-odor properties, particularly long lasting and wash durable antimicrobial and/or anti-odor properties, may be imparted to fabrics.
There especially remains a need for a method, especially a simple and cost effective method, by which antimicrobial and/or anti-odor properties, particularly long lasting and wash durable antimicrobial and/or anti-odor properties, may be imparted to sulfur containing and/or sulfur treated fabrics.